Extra-Solar Planets

The detection and study of extra-solar planetary (exoplanet) systems is a relatively new and exciting field of astrophysics. Since 1995 more than 500 extra-solar planets have been discovered and the rate of detection is accelerating as methods improve.

At JBCA we are engaged in the detection and study of exoplanets using two complementary detection methods: gravitational microlensing and the transit method. We also have more general interests in the architecture of exoplanetary systems, planet formation theories and how these can be directly tested by exoplanet observations.

A time lapse of the night sky over the Danish Telescope at La Silla during MiNDSTEp observations by the JBCA exoplanets group. The Galactic Centre comes into view over head towards the end of the movie.

Staff at JBCA are leaders in theoretical and observational aspects of exoplanet detection using microlensing. In the context of exoplanet detection microlensing describes the temporary magnification of background stars by the passage of foreground planetary systems across the line of sight. The plantary host star produces a magnification signal which typically lasts for weeks to months, whilst its planets may induce brief distortions of this signal lasting for around a day (for a Jupiter mass planet) down to hours (for Earth mass planets). Microlensing is especially good for detecting low-mass planets at large separations from the host star, a regime that is difficult to explore with other detectiion methods. JBCA staff have close links with the main microlensing survey groups (OGLE and MOA). We are also members of the MiNDSTEp follow-up network which uses telescopes based in Chile, South Africa and the USA to look for signals due to exoplanets down to Earth masses. Staff at JBCA have pioneered both the theory behind extra-solar planet detection with microlensing, as well as the theory and application of the technique beyond the Milky Way. Research programmes in this area at JBCA span observations, data reduction techniques, analysis and theory.

Dr Eamonn Kerins is a co-leader of the ESA Euclid Exoplanets Working Group. ESA has recently selected Euclid as a medium-class mission in its Cosmic Vision programme. Euclid's primary science is the study of dark energy but it is also expected to undertake other science programmes including a high cadence near-infrared search for exoplanets towards the Galactic bulge using microlensing. Such a survey would allow the distribution function of exoplanets to be determined down to Earth masses over exoplanet host separations ranging from 0.5 AU out to the free-floating exoplanet regime, providing the ideal complementary dataset to Kepler. Manchester is a World leader in simulations of space-based microlensing surveys and we are leading the design of the Euclid exoplanet survey.

Members of JBCA are also engaged in the detection of exoplanets using the transit method. If a planet passes directly in front of its parent star then the brightness of the host star will temporarily decrease. The decrease is typically very small: the brightness of a Sun-like star will drop by only 1% due to the passage of a Jupiter-like planet across it. To date over one hundred planets have been detected in this way. The transit method is especially sensitive to planets closer to their host star, where the probability of transit is hightest, and so provides excellent complementarity with the microlensing method described above. JBCA members are involved in MiNDSTEp which uses both microlensing and transits to detect exoplanets.

Our interest in planet formation stems from involvment in the PEBBLES collaboration, together with colleagues from St Andrews and Edinburgh universities. PEBBLES will use eMerlin and ALMA to image planet growth in the 'missing link' size range between tiny dust grains and planets large enough to be detected by microlensing, transit observations, or other methods.